Field of the Invention
The present invention relates to an exhaust device for an engine provided with a turbo supercharger.
Background Art
In recent years, an engine provided with a turbo supercharger has been paid attention to in view of a demand for downsizing. Japanese Patent No. 4803059 discloses an engine provided with a cylinder head in which an exhaust manifold is integrally formed; a turbo supercharger which is fixed to a side surface of the cylinder head and communicates with a gathering portion of the exhaust manifold; and an exhaust pipe provided with a catalyst device and coupled to the turbo supercharger in the cylinder array direction.
The engine structure as described above is advantageous in making the engine as a whole compact while enhancing the supercharging pressure characteristics of the engine, and in reducing the number of assembling steps, as compared with an engine provided with an exhaust manifold separately from a cylinder head. Further, high-temperature exhaust gas discharged from the cylinder head is fed to the catalyst device only through the turbo supercharger. Therefore, the engine structure is also advantageous in the aspect of promoting activation of the catalyst device.
In an engine, it is important to reduce NOx (nitrogen oxide) in exhaust gas. As one of the measures, it is effective to carry out EGR (Exhaust Gas Recirculation) control of recirculating part of exhaust gas to an intake passage. Further, in some cases, it is necessary to provide an exhaust gas processing device in order to trap fine particles such as soot contained in the exhaust gas. There is an idea of carrying out EGR control or trapping fine particles within exhaust gas in order to improve exhaust gas characteristics, as well as in the engine disclosed in Japanese Patent No. 4803059. In such a case, it is important to dispose an EGR device and an exhaust gas processing device in a compact manner, taking into consideration a positional relationship with respect to a turbo supercharger and a catalyst device in order to make the engine compact. Japanese Patent No. 4803059, however, fails to disclose the above point.
When EGR control is carried out, the combustion temperature is lowered, which may lower the temperature of exhaust gas. This may make it difficult to activate the exhaust gas purification catalyst. The same problem as described above may also occur in a diesel engine having a high combustion efficiency. In view of the above, it is desirable to provide a configuration advantageous in activating a catalyst device and the like when an EGR device and an exhaust gas purification device are provided.